1. Field of the Invention
The present invention relates generally to damping devices, and more particularly, but not by way of limitation, to an improved semi-active vibration mitigation assembly for suppressing vibrations of civil structures.
2. Description of Related Art
In recent years, an intensive effort has been made to develop vibration damping systems for civil structures, such as buildings and bridges, which are both economical and efficient for mitigating vibrations produced by dynamic disturbances, such as wind, vehicle loads, and seismic activity. Past efforts have produced a range of designs that include fully active vibration mitigation systems, passive vibration mitigation systems, and hybrid or semi-active vibration mitigation systems.
Active vibration mitigation systems utilize large electric motors and costly hydraulic pumping equipment to provide force inputs to a structure during a dynamic event. Passive damping systems, on the other hand, require no power and are less expensive to operate than active damping systems. However, passive vibration mitigation systems are incapable of providing the structural protection desired. Semi-active vibration mitigation systems provide a much needed middle ground between active and passive vibration mitigation systems.
The power required to operate a semi-active vibration mitigation system is low relative to the amount of energy dissipated; whereas, the amount of power required to operate a fully active vibration mitigation systems is approximately equal to or greather than the amount of energy to be dissipated.
The hardware utilized in semi-active vibration mitigation systems generally includes a high pressure hydraulic cylinder with a piston slidably disposed therein so as to form a fluid-filled chamber in each end of the cylinder. To permit fluid to flow from one chamber to the other, the chambers are fluidly interconnected with plumbing. A control valve is interposed in the plumbing to control the flow of fluid between the chambers.
Energy is dissipated from the structure to which the semi-active vibration mitigation system is connected by actuating the control valve so as to vary the flow area of the valve. The valve is actuated by control signals generated by a controller in response to data obtained from structural motion sensing devices, such as accelerometers and strain gauges, and from pressure data obtained from sensors attached to the hydraulic system. The choice of the control algorithm employed is critical to providing a stable and effective vibration mitigation system.
Previous semi-active vibration mitigation designs have utilized expensive and complex hardware and have failed to take into account certain critical variables when generating a control signal. Most particularly, previous designs have failed to consider the effects of the compressibility of the fluid. The variable stiffness of the hydraulic fluid affords an opportunity to store and release elastic energy. The capacity to both store and dissipate energy differentiates the semi-active damping assembly proposed herein from variable damping systems that have previously been employed in automotive and civil structure applications. The design proposed herein provides for the automatic regulation of the energy stored and dissipated in order to mitigate structural vibration effectively.